Anesthetics have been in clinical use for nearly 100 years, but their mechanism of action is still unknown. Effect of anesthetics such as alcohols, barbiturate on fluorescence intensity decay of multitryptophan protein PM ATPase of has been studied. Time-resolved fluorescence confirms the diffusional character of the fluorescence quenching. Quenching is most effective on surface exposed tryptophans. Information on the effects of anesthetics on membrane-bound proteins may provide insights into the mechanism of action.[unreadable]